'Abdullah bin 'Amr bin Al-'As (May Allah be pleased with them) reported:
The Messenger of Allah (ﷺ) said, "Allah forgives every sin of a martyr, except his debt."[Muslim].Another narration in Muslim is: The Messenger of Allah (ﷺ) said, "Being martyred in the Cause of Allah expiates for everything, except debt." (PT)
App reference (PT): Book 12, Hadith 28 (PT)
Arabic/English book reference (PT): Book 12, Hadith 1312 (PT)